Inflammatory immune responses are associated with IL-12, TNF, IL-1, and other cytokines. These cytokines are rapidly produced by bacteria and bacterial components, such as DNA and LPS. Manufacture of plasma derivatives involves steps which are not aseptic and which can lead to bacterial contamination. The intact bacteria are removed by sterile filtration, but this step does not remove LPS or bacterial DNA (bDNA), or other microbial molecules. Adverse events with IGIV administration include fever and hypotension; fever has been associated with elevated TNF levels in recipients, and hypotension is a known side effect of LPS. It was of interest to determine whether the pattern of cytokine secretion by human monocytes was similar after IGIV and microbial stimulation of cells, and whether the low levels of LPS and bDNA present in IGIV were sufficient to stimulate cytokine release. Multiple lots of IGIV from different manufacturers were assessed to determine whether they could stimulate TNF or IL-1 release from human mononuclear cells at concentrations that are present in humans after IGIV infusion. Most lots stimulated significant TNF production, which was most consistently observed when non-heat inactivated human serum was used in the culture media. Although no IGIV lots had LPS contamination > 0.91 EU/ml (the industry standard), dose response experiments using LPS showed that amounts lower than 0.91 EU/ml can stimulate cytokine release from monocytes. Bacterial DNA was also detected in IGIV using PCR primers which recognized broadly conserved bacterial DNA sequences; the levels detected were lower than those needed to stimulate monocyte cytokines in vitro. However, the presence of bDNA suggests that other bacterial constituents could also be present, some of which may not be detected by current lot release standards such as LPS testing and rabbit pyrogen testing. Future work is planned to focus upon better and more standardized methods of screening IGIV for the presence of microbial constituents, using stable cell lines and flow cytometry.